I added a variable (Xc), along the lines of what barney suggested, to capture the "concentration effect" of the top ~1-3 teams in GF. Xc is defined as the % of players in the top 1N who were on the top 0.1N teams in GF.

More recently, variables which measure expansion (% of new teams in past 1 or 2 seasons) and the effect of non-Canadians on the top 1N scoring average.

Y: avg. simple adjusted points (gms, GPG, A/G) of top 1N players (N=number of teams)
B0: Y-intercept (constant)
Xn: Number of teams
Xh: Fraction of new teams vs. previous season
Xi: Fraction of new teams vs. two seasons previous
Xg: League GPG
Xp: PP opportunities/game
Xf: Standard deviation of teams' GF, divided by avg. team GF
Xa: Standard deviation of teams' GA, divided by avg. team GA
Xt: Excess above avg. GF of top 0.2N teams in GF, divided by std dev of team GF
Xc: Ratio of players in top 1N which were on teams in the top 0.1N in GF
Xe: Fractional increase in avg. of top 1N due to non-Canadian players

One important factor that may still be missing is the presence/absence of some of the very top Canadian players (i.e., Gretzky and/or Lemieux). It will probably take a lot of trial and error to determine how to best define the proper variable to capture this causality.